There are not too many breeds of dog that are friendlier than the Labrador (B).
Since we are comparing all breeds of dogs to the labrador, we need to use a comparative adjective. If we were saying that Labradors are the friendliest breed of dogs, this would be the superlative. In the comparative, we have to add -er to the verb if it is one or two syllables long. We add more when it is three or more syllables long. Since friendly is only two syllables, we need to change "more friendly" to "friendlier." Also, it does not make since to use the past tense, so we need to change were to are.